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How do the instructions included with the meter know what kind of plane you have and how it was deisigned? Incidences can vary on planes. Different airfoils, different designs and so on will dictate how it is set up. Sure, your plane COULD be designed to have the wing and stab exactly parallel but then again, maybe not. Look at various airplane plans and you'll see how these things can really vary. As has been suggested, the incidence should be altered only in response to flight characteristics, especially when the intended design is a complete unknown.

Personall, I think your CG is too far rearward. I could be wrong of course since I haven't actually seen or flown the plane.

To be honest all this talk of incidences and thrust angles is probably a little advanced for the beginners forum too.

If this Decathalon is too much trouble, I'd be tempted to shelve it myself. Take alook at a good handling plane such as the Tiger-2 or World Models T-34. Heck, even a World Models Mach-1 is a very aerobatic, great handling plane. Neither are really scale but they fly great. Plus, if your goal is to someday compete in pattern, you won't have a scale plane for that either. Both airplanes would do well in sportsman competition plus be appropriate for your experience level. They'll teach you a lot. The GP Cherokee might be another good option but it is a little on the porky side and can land hot if you aren't careful. The flaps help tremendously of course but just add another level of unnecessary complexity for a beginner in my opinion.